Mechanisms that govern the phenotypic specification and expression of neural crest-derived peripheral neurons are beginning to be elucidated. Rules governing the interaction between progenitor cells and their microenvironment will be important in understanding how the nervous system develops. Neural crest-derived cells constitute the majority of neurons and support cells of the peripheral nervous system but the interactions between these cells and growth factors that regulate the molecular composition of their microenvironment remain poorly understood. The neural crest of mammalian (mouse) and avian (quail or chick) species is a good model system for aspects of human development pertaining to cell-cell interactions and factors governing cell lineage specification and phenotypic expression. Transforming growth factor beta (TGF-beta) is a growth and differentiation factor that shows appropriate spatial and temporal expression to postulate a role in neural crest cell development. TGF-beta affects the expression of extracellular matrix molecules such as laminin and collagen type IV which have been implicated in aganglionosis of the terminal bowel of the lethal spotted (ls/ls) mutant mouse. Use of the ls/ls mouse as a model for aganglionosis (typical of Hirschsprungs disease in humans) will make it possible to ask questions both in-vitro and in-situ about the role of the extracellular matrix in neural crest cell migration and differentiation. Dispersed neural crest cells, organ cultures of tissue previously colonized by neural crest cells and in-situ models, all of which are well suited to the combined biochemical and molecular approaches required for addressing issues of cell migration, differentiation and lineage segregation will be employed. The effects of TGF-beta on expression of extracellular matrix molecules (ECM) by mesenchymal cells located along neural crest cell migration pathways as well as the expression of integrins, a family of cell surface ECM molecule receptors, on neural crest and neural crest derived neurons and glial cells will be studied. The ability of neural crest cells to colonize tissues whose expression of ECM has been altered by TGF-beta will be assessed. Altering ECM expression by TGF-beta, in tissue culture, will make it possible to ask questions on biochemical and molecular levels about the spatial and temporal expression of ECM molecules and evaluate their effect on neural crest cell migration and differentiation. Experiments will seek to distinguish those effects on neural crest-derived cells of TGF-beta that are mediated through the ECM from possible direct action of TGF-beta on the neural crest-derived cells themselves. The experiments will provide new insights into the ways in which neural crest cell migration and differentiation can be modified by growth factors that affect ECM expression.